In the field of mobile communication technologies, research and development of next generation communication systems are being conducted at a rapid pace. In a candidate next generation communication system, a single-carrier scheme is to be used for uplink to reduce the peak-to-average power ratio (PAPR) while achieving wide coverage. Also in this communication system, uplink and downlink radio resources are allocated to users according to their communication conditions in the form of shared channels to be shared by the users. The process of allocating radio resources is called “scheduling”. In order to perform uplink scheduling properly, each user device transmits a pilot channel to a base station and the base station estimates uplink channel conditions of the user device based on the reception quality of the pilot channel. Similarly, in order to perform downlink scheduling properly, the base station transmits a pilot channel to the user device and the user device reports information indicating channel conditions (channel quality indicator (CQI)) to the base station based on the reception quality of the pilot channel. The base station evaluates downlink channel conditions of user devices based on CQIs reported from the user devices and performs downlink scheduling based on the evaluation results.
Meanwhile, uplink control channels may be categorized into first control information (essential control information) that is always sent together with an uplink data channel and second control information that is sent regardless of the presence or absence of an uplink data channel. The first control information includes information that is necessary to demodulate a data channel such as the modulation scheme and the channel coding rate of the data channel. The second control information includes a downlink CQI, acknowledgement information (ACK/NACK) for a downlink data channel, and/or a resource allocation request. A user device may transmit only the first control information, only the second control information, or both of them via an uplink control channel.
In a proposed method, when a resource block (radio resources) is allocated for transmission of an uplink data channel, the first control information (and also the second control information if necessary) is transmitted using the allocated resource block; and when no uplink data channel is to be transmitted, the second control information is transmitted using dedicated resources (dedicated frequency band). This method is described below in more detail.
FIG. 1 is a drawing illustrating an example of uplink frequency band allocation. In FIG. 1, two sizes of resource blocks, large and small, are provided. The large resource blocks have a bandwidth FRB1 of 1.25 MHz and a time period TRB of 0.5 ms. The small resource blocks have a bandwidth FRB2 of 375 kHz and a time period TRB of 0.5 ms. The time period may also be called a unit transmission period, a transmission time interval (TTI), or a subframe. One time period may correspond to the duration of one wireless packet. In FIG. 1, six resource blocks are arranged in the frequency direction and the small resource blocks are located at the right and left ends. Various arrangement patterns may be used to arrange resource blocks as long as they are known to the sending and receiving ends. In the example shown in FIG. 1, uplink scheduling is performed such that control channels (first control channels) accompanying uplink data channels and if necessary, second control channels are transmitted in parts of the time periods of the respective large resource blocks (the second, third, fourth, and fifth resource blocks). Also, transmission timings of user devices are adjusted such that control channels (second control channels) are transmitted using the small resource blocks (the first and sixth resource blocks) when uplink data channels are not to be transmitted. A second control channel of a user device may be transmitted using two small resource blocks. In this example, the second control channel of user device A is transmitted using the sixth resource block in the second subframe and the first resource block in the third subframe. Similarly, the second control channel of user device B is transmitted using the sixth resource block in the third subframe and the first resource block in the fourth subframe. Thus, a second control channel is transmitted so as to “hop” in the frequency and time directions. This method makes it possible to achieve time and frequency diversity gain and to increase the probability that the second control channel is properly demodulated by the base station.
FIG. 2 is a drawing illustrating another example of uplink frequency band allocation. As in FIG. 1, two sizes of resource blocks, large and small, are provided in FIG. 2. In this example, a time period TRB of each subframe of the small resource blocks (first and sixth resource blocks) is divided into two sub-periods. In FIG. 2, the second control channel of user device A is transmitted using the first resource block in a first sub-period (the first half) of the first subframe and the sixth resource block in a second sub-period (the second half) of the same first subframe. Similarly, the second control channel of user device B is transmitted using the sixth resource block in the first sub-period of the first subframe and the first resource block in the second sub-period of the first subframe. The second control channels of user devices A and B are also transmitted in a similar manner in the third and fifth subframes. Thus, a second control channel is transmitted so as to “hop” in the frequency and time directions. This method makes it possible to achieve time and frequency diversity gain and to increase the probability that the second control channel is properly demodulated by the base station. Also with this method, transmission of a control channel of user device A is completed within one subframe and transmission of a control channel of user device B is also completed within one subframe. Therefore, this method is preferable to reduce transmission delay of uplink control channels. The above technologies are disclosed, for example, in 3GPP, R1-061675.